At present, one of the most common methods relies on UV rays to remove contaminants from water. However given that ultraviolet rays comprise less than 4-percent of the solar radiation reaching Earth, this particular approach usually takes up to two whole days to complete, making it less suitable for use in developing countries where a large portion of the population has to walk several miles every day to collect safe, drinking water.

For the research, scientists from Stanford University worked alongside SLAC National Accelerator Laboratory to build an ingenious water purification device that is significantly faster and more efficient than currently available technologies. Instead of using UV rays, the new contraption relies on the visible part of the solar spectrum for its functions. This in turn allows us to harness nearly 50-percent of the incident solar energy. Speaking about the project, recently published in the Nature Nanotechnology journal, Chong Liu said:

Our device looks like a little rectangle of black glass. We just dropped it into the water and put everything under the sun, and the sun did all the work.

When dropped into a container full of water, this small contraption uses sun’s energy to purify the liquid within minutes. Measuring around half the size of a postage stamp, the device produces an array of bacteria-killing compounds, including hydrogen peroxide, when exposed to sunlight. These chemicals, according to the researchers, are capable of annihilating up to 99-percent of the bacteria floating in the water sample. What’s more, it only takes 20 minutes for the disinfection process to complete, following which the chemicals automatically dissipate.

The device features a small glass sheet covered with what they are calling “nanoflakes” of molybdenum disulfide. These nanostructurres are stacked one on top of the other in a sort of labyrinthine pattern, similar to the ridges of a fingerprint. As pointed out by the scientists, MoS2 commonly serves as an industrial lubricant. When shaped into minuscule flakes, however, it acts as a photocatalyst, facilitating chemical reactions in presence of light.

By arranging the flakes in a specific pattern, the team was able to ensure the absorption of the full spectrum of visible sunlight. This in turn facilitated reactions with oxygen as one of the reactants, leading to the production of hydrogen peroxide and other anti-bacterial chemicals. It is important to note, however, that the contraption is not suited for eliminating pollutants, other than microbes, from water.

As explained by the team, the new device can be used in areas, where water is mostly contaminated with disease-causing bacteria and other micro organisms. The scientists are currently testing the technology against various strains of bacteria. Liu added:

It’s very exciting to see that by just designing a material you can achieve a good performance. It really works. Our intention is to solve environmental pollution problems so people can live better.